Hydrogenation of low rank coal

ABSTRACT

LOW RANK COAL HAVING A HIGH OXYGEN CONTENT IS HYDROGENATED INTO HYDROCARBONACEOUS PRODUCTS WHILE REDURING THE HYDROGEN CONSUMPTION BY CONDUCTING THE HYDROGENATION OF SUCH COAL IN FIRST AND SECOND STAGE EBULLATED BED REACTION ZONES WITH THE SEPARATE WITHDRAWAL OF THE GASIFORM EFFUENT STREAM CONTAINING CARBON MONOXIDE AND CARBON DIOXIDE BETWEEN THE FIRST AND SECOND HYDROGENATION STAGES.

United States Patent 3,700,584 HYDROGENATION OF LOW RANK COAL Edwin S. Johanson, Princeton, Ronald H. Wolk, Lawrence Township, and Clarence A. Johnson, Princeton, N.J., assignors to Hydrocarbon Research, Inc., New York,

Filed Feb. 24, 1971, Ser. No. 118,225 Int. Cl. Cg 1/08 US. Cl. 208-10 ABSTRACT OF THE DISCLOSURE Low rank coal having a high oxygen content is hydrogenated into hydrocarbonaceous products while reducing the hydrogen consumption by conducting the hydrogenation of such coal in first and second stage ebullated bed reaction zones with the separate withdrawal of the gasiform effluent stream containing carbon monoxide and carbon dioxide between the first and second hydrogenation stages.

BACKGROUND OF THE INVENTION SUMMARY OF THE INVENTION Accordingly, it is the principal object of the present invention to provide a process for reducing the hydrogen consumption in the ebullated bed hydrogenation of low rank coal having a high oxygen content.

It is our theory that the high consumption of hydrogen during the ebnllated bed hydrogenation of low rank coal having a high oxygen content is due to the large amounts of carbon monoxide and especially carbon dioxide gaseous by-products generated during the first stages of hydrogenation reaction in the course of eliminating the oxygen from the low rank coal. It is though that the carbon monoxide and carbon dioxide by-products then react with the hydrogen and hence consume it in accordance with the following equations:

Such a theoretical explanation of the high hydrogen consumption is believed to be verified by the fact that the hydrogenation in a single stage ebullated bed hydrogenation zone of a low rank coal having a high oxygen content at a coal feed rate designed to give high conversion of coal, results in products which upon analysis, are shown to contain large quantities of Water and small quantities of carbon monoxide and carbon dioxide, while such hydrogenation at a higher feed rate designed to give only partial conversion of coal produces more carbon oxides and less water. The chemical principal of the conversion of carbon oxides to hydrocarbons and water is well established; but there has been no new teaching in the art of coal hydrogenation that leads to the unexpected results that these reactions can be supported by coal hydrogenation catalysts in the milieu of the coal hydrogenation reactor at a rate suflicient to significantly alter the product structure and hydrogen requirement.

12 Claims- "ice In accordance with the process of the present invention, a low rank coal having a high oxygen content is hydrogenated using both first stage and second stage ebullated bed reaction zones with the separate withdrawal of the gasiform efiluent stream containing carbon monoxide and carbon dioxide gases between the two stages. More particularly, in the process of the present invention a low rank coal having a high oxygen content is prepared for hydrogenation by drying, grinding and screening the coal to form a coal feed which is thereafter slurried with a slurry oil liquid produced in the process. The slurry is partially hydrogenated in a first stage ebullated bed reaction zone with hydrogen in the presence of ebullated hydrogenation catalyst particles. A gasiform efiluent stream containing carbon monoxide and carbon dioxide and a partially unreacted coal-containing liquid effluent stream are separately withdrawn from the first stage zone. The partially unreacted coal-containing liquid efliuent stream is then further hydrogenated in a second stage ebullated bed reaction zone with hydrogen in the presence of ebullated hydrogenation catalyst particles. A gasiform effluent stream and solids-containing liquid efiluent stream are separately withdrawn from the second stage zone. Thereafter, hydrocarbonaceous products are recovered from the gasiform effluent streams of the first and second stage zones and from the solids-containing liquid eflluent stream of the second stage zone.

Further details and suitable operating parameters for the process of the invention are described hereinafter.

DESCRIPTION OF THE DRAWING The drawing is a diagrammatic view, partly in section, of typical process equipment suitable for practicing the process of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS As shown, a low rank coal, i.e., sub-bituminous coal, brown coal, or lignite, having a high oxygen content of at least about 15% by weight on the weight of the dry coal entering the system at 10 is first passed through a preparation unit generally indicated at 12. In such a unit it is desirable to dry the low rank coal of all surface moisture and to grind the coal to a desired mesh and to screen it for uniformity. For our purposes, it is preferable that the low rank coal has a particle size between about 20 to about 200 Tyler mesh, i.e., the coal particles all pass through a 20 mesh Tyler screen and substantially all (not less than of the coal particles are retained on a 200 mesh Tyler screen. However, it will be observed that the preciseness of size may vary between different types of low rank coal. For most cases, this size range is preferable in that it is of sutlicient fineness for adequate reactivity without incurring excessing costs in pulverizing, but does not preclude the use of finer materials when required.

The coal particles discharge at 14 into the slurry tank 16 where the coal is blended with a carrying or slurry oil indicated at 18 which, as hereinafter pointed out, is conveniently made in the system. To establish an effective transportable slurry, it has been found that the ground low rank coal should be mixed with at least about an equal weight of carrying oil and usually not more than 10 parts of oil per part of coal. In addition, the hydrogenation catalyst, may be added at 20, if desired, in ratio of about 0.01 to about 2.0 pounds of catalyst per ton of coal. Such a catalyst would be from the class of cobalt, molybdenum, nickel, tin, iron and the like deposited on a base of the class of alumina, magnesia, silica, and the like. It is to be noted that the catalyst need not be added continuously nor is it required that it be in fine admixture with the low rank coal, in that it can be added to the reactor independently of the coal at 32 or 54.

The coal-oil slurry is then passed via line 21 through the heater 22 to bring the slurry up to reaction temperature, such heated slurry then discharging at 24 into the first stage reaction zone feed line 26 wherein it is supplied with make-up hydrogen from line 28 as well as recycled hydrogen in line 72.

The entire mixture of hydrogen and coal-oil slurry then enters a first stage ebullated bed reaction zone 30 passing upwardly from the bottom at a rate and under pressure and at a temperature to accomplish partial hydrogenation. The first stage ebullated bed reaction zone 30 is first charged with hydrogenation catalyst particles via line 32. Replacement catalyst can also be added via line 32. The spent hydrogenation catalyst particles can be periodically withdrawn from the first stage ebullated bed reaction zone 30 via line 34 for disposal or alternately regeneration and reuse of the spent catalyst.

By concurrently of liquid and gasiform materials upwardly through a vessel containing a mass of solid particles of a contact material, which may be a specific catalyst as above indicated, and expanding the mass of solid particles at least over the volume of the stationary mass, the particles are placed in random motion within the vessel by the upflowing streams. A mass of solid particles in the state of random motion in a liquid medium may be described as ebullated. The characteristics of the ebullated mass at a prescribed degree of volume expansion can be such that a finer, lighter solid may pass upwardly through the mass so that the particles constituting the ebullated mass are retained in the first stage reaction zone and the finer, lighter material may pass from the first stage reaction zone.

The contact material (herein hydrogenation catalyst) is preferably in the form of beads, pellets, lumps, chips or like particles at least about inch and more frequently in the range of A to A; inch (i.e., between about 6 and 30 mesh screens of the Tyler scale). The size and shape of the particles used in any specific process will depend on the particular conditions of that process, e.g., the density, velocity and viscosity of the liquid involved in that process.

It is a relatively simple matter to determine for any ebullated process the range of throughput rates of upflowing liquid which will cause the mass of solid contact or catalyst particles to become expanded and at the same time placed in random motion. The gross volume of the mass of contact or catalyst particles expands when ebullated without, however, any substantial quantity of the particles being carried away by the up-flowing liquid and, therefore, a fairly well defined upper level of randomly moving particles establishes itself in the upfiowing liquid. The upper level 36 above which few, if any, particles ascend will hereinafter be called the upper level of ebullation.

In contrast to processes in which fluid streams flow downwardly or upwardly through a fixed mass of particles, the spaces between the particles of an ebullated mass are thus large with the result that the pressure drop of the liquid flowing through the ebullated mass is small and remains substantially constant so the fluid throughput rate is increased. Thus, a considerably smaller consumption of power is required for a given throughput rate. Moreover, the ebullated mass of particles promotes much better contact between the coal fines and gasiform streams than with any fixed bed process. Under these conditions, a significantly greater fluid throughput rate carrying the coal fines may be used without impairing the desired degree of contact than if conventional downfiow or upfiow through a fixed bed of contact particles is used.

Moreover, solid material will pass through an ebullated bed where it would otherwise plug a fixed bed. Additiona ly, the random motion of particles in an ebullated mass causes these cont-act particles to rub against each other and against the walls of the 'vessel so that the formation of deposits thereon is impeded or minimized. The scouring action helps to prevent agglomeration of the contact or catalyst particles and plugging up of the vessel. This effect is particularly important where catalyst particles are employed and maximum contact between coal fines, hydrogen and the catalytic surfaces is desired, since the contact surfaces are exposed to reactants for a greater period of time before becoming fouled or inactivated by foreign deposits.

The process of the invention may be carried out under a wide variety of conditions. To obtain the advantages of this invention it is only necessary that the liquid, low rank coal fines, and gasiform materials flow upwardly through a mass of solid particles of a contact material at a rate causing the mass to reach an ebullated state. In each ebullated system, variables which may be adjusted to attain the desired ebullation include the flow rate, density and viscosity of the liquid and gasiform material, and the size, shape and density of the particulate material. However, it is a relatively simple matter to operate any particular process so as to cause the mass of contact material employed to become ebullated and to calculate the percent expansion of the ebullated mass after observing its upper level of ebullation through a glass window in the vessel, or by radiation or acoustic permeability, or by other means such as liquid samples drawn from the vessel at various levels. In general, the gross density of the stationary mass of contact material will be between about 25 to about 200 pounds per cubic foot, the flow rate of the liquid between about 5 and about gallons per minute per square foot of horizontal cross-section of the ebullated mass, and the expanded volume of the ebullated mass usually not more than about double the volume of the settled mass and preferably only about 30 to 50 percent greater than the settled volume.

Liquid may 'be recycled internally within the reaction zone 30; in such case, a standpipe 38 with a top open end above the upper evel of ebullation 36 may be used to pass liquid from the top of the reaction zone 30 to pump 40 disposed below distributor plate 42 in the bottom of the reaction zone 30, the liquid discharged by the submerged pump thence flowing upwardly again through the mass of ebullated solids.

Operating conditions of temperature and pressure in the first stage reaction zone 30 are in the range of from about 750 F. to about 950 F., preferably from about 825 F. to about 925 F., and at a pressure of from about 1000 to about 3000 p.s.i.g.

In the first stage reaction zone 30 the coal-oil slurry is partially hydrogenated. A gasiform eflluent stream containing carbon monoxide and carbon dioxide by-products is separately withdrawn from the top of reaction zone 30 via line 46 and a partially unreacted coal-containing liquid eflluent stream is withdrawn from reaction zone 30 above the top of the expanded ebullated bed 36 via line 44 and fed to feed line 48 of a second stage ebullated bed reaction zone 50.

Make-up hydrogen is fed into the second stage reaction zone 50 via line 52 as well as recycled hydrogen in line 73. A hydrogenation catalyst bed is provided in the second stage reaction zone 50 by feeding the catalyst therein via line 54. Spent catalyst can be withdrawn from the reaction zone via line 56 and for disposal or alternately regenerated and re-fed to the reaction zone. The upper level of ebullation in reaction zone 50 is indicated at 58.

The second stage reaction zone 50 can be operated under the same operating conditions of temperature, pressure, liquid feed rate and catalyst as given above for the first stage reaction zone 30 and it can be provided with a standpipe 60, pump 62 and distributor 64 for internal recycle of liquid to maintain the desired superficial liquid velocity. External recycle of liquid can also be employed. Heat tempering to achieve the desired first and second stage temperatures is accomplished by adjusting the preheats of make-up and recycled hydrogen in heaters 78 and 80.

The coal feed rate through the first stage reaction zone 30 and the second stage reaction zone 50 is from about to about 100 pounds per hour per total cubic feet of the two reaction zones 30 and 50. The total hydrogen feed rate through both the first and second stage reaction zones 30 and 50 is generally from about to about 60 standard cubic feet per pound of coal and the separate hydrogen feed rate in each of said two zones is directly proportional to the zone volume of size thereof. With this pattern of hydrogen flow approximately equal dilution of the hydrogen will occur in each stage by the gasiform products of coal conversion. The ratio of the first stage reaction zone 30 to the volume or size of the second stage reaction zone 50 generally is from about 1:4 to about 3 :1 and preferably is about 1:2.

While all proportions of first stage to second stage volume will result in hydrogen economy from the considerations put forth in this invention, the optimum economic performance will usually be obtained with the first stage as the smaller of the two reactors. Maximum carbon dioxide production and hydrogen economy may occur with as low a first stage volume as 10 percent of the total; but the stability and performance of the ebullated bed is adversely efiected by low coal conversion level resulting in operating the first stage at such a low residence time. The proportions of first and second stage volume proposed here will achieve at least 90 percent of the potential hydrogen economy possible by a stage system at conversion levels affording good operability.

Thus, where the volume of the second stage reaction zone 50 is twice that of the first stage reaction zone 30 and where the total hydrogen feed rate through both of the two reaction zones 30 and 50 is about 30 standard cubic feet per pound of coal, the directly proportional separate hydrogen feed rate through the first stage reaction zone 30 is about 10 standard cubic feet per pound of coal and in the second stage reaction zone 50 is about 20 standard cubic feet per pound of coal. It will be appreciated, however, that the first and/or second stage reaction zones 30 and 50 can be constituted of a single ebullated bed reactor each or a plurality of ebullated bed reactors in parallel. For example, and for reasons of economy in equipment costs, the first stage reaction zone 30 can be a single ebullated bed reactor and the second stage reaction zone 50 can be two ebullated bed reactors arranged in parallel, with all three ebullated bed reactors being of equal size or volume. In such an arrangement, the ratio of volume or size of the first stage reaction zone to the volume or size of the second stage reaction zone would be 1:2 and where the total hydrogen feed rate through both the first and second stage reaction zones is about 30 standard cubic feet per pound of coal, the directly proportional separate hydrogen feed rate to each of the three equivolume reactors would be 10 standard cubic feet per pound of coal.

In the second stage reaction zone 50 the partially unreacted coal-containing liquid effluent stream from first stage reaction zone 30 fed to the second stage reaction zone 50 via lines 44 and 48 is further hydrogenated. A gasiform efiiuent stream is separately withdrawn from the top of the second stage reaction zone 50 via line 66. The gasiform efiluent streams from the first and second stage reaction zones 30 and 50 are passed via manifold line 68 to a separates 70 wherein hydrocarbonaceous vapors, any entrained solids, carbon monoxide and carbon dioxide gases and excess hydrogen gas can be separated from one another to the extent desired and the recovered hydrogen gas recycled to the first stage reaction zone 30 via line 72. If desired, recovered hydrogen gas can also be recycled to the second stage reaction zone.

A solids-containing liquid efliuent stream is separately withdrawn from the second stage reaction zone 50 via line 74 and fed to a recovery unit 76 for recovery and separation for hydrocarbonaceous and other products, such as gasoline, fuel oil, residual oil, char, and the like. A fraction of the recovered oil product, such as No. 4 fuel oil, can be used as the slurry oil tank 16 via line 18.

The process of the invention will be further illustrated by the following representative example thereof.

Example 1 Australian brown coal having the following analysis was treated in accordance with the above described two stage process of the invention:

The most noteworthy characteristic of the brown coal is its very high organic oxygen content, nominally 23.2% on the dry basis. The true organic oxygen content is somewhat higher, because of the character of the mineral matter. The mineral matter is predominantly lime and magnesia, and, in the conventional coal analysis for ash, a substantial part of these compounds are converted to the respective sulfates, which would explain why the ashes contain sulfur equivalent to 0.91 wt. percent of the dry coal, while the identified mineral sulfur (pyritic and sulfate) amounts to only 0.35 wt. percent of dry coal. The additional sulfur and the oxygen required for sulfate formation are equivalent to about 1.9 wt. percent of the dry coal, and would correspond to a decrease of the ash percentage to give original mineral matter and an increase in nominal organic oxygen by the same amount.

The exemplary operating parameters for the two stage process of the invention were as follows:

TAB LE II Coal feed 20-200 Tyler mesh particles. Goal to slurry 011 weight ratio 1:1 (The amount in excess of 1 is recycled slurry.) Coal feed rate through first and 31.2 pounds per hour per total second stage reaction zones. cubic feet of the two stage Particles of cobalt molybdate on alumina of uniform cylindrical size about 0.06 inch in diameter and $4; inch in length.

850 F., 2,250 p.s.i.g.

20 gallons per minute per square foot of horizontal cross-section zones. thereof Total hydrogen feed rate through 35 standard cubic feet per pound both the first and second stage of coal. reaction zones.

Hydrogen feed rate through first 11.7 standard cubic feet per stage reaction zone. pound of co Hydrogen feed rate through second 23.4 standard cubic feet per stage reaction zone. pound of coal.

A comparative run was made on the same Australian brown coal using only a single stage reaction zone having a volume or size equal to the total volume or size of both the first and second stage reaction zones 30 and 50 utilized in the above illustrative example of the two stage process of ,the invention. In this comparative run the operating parameters were otherwise the same as those given above in Table II with the additional exception that the hydrogen feed rate to the single stage reaction zone was 35 standard cubic feet per pound of coal and hence was equal to the total hydrogen feed rate through both the first and second stage reaction zones 30 and 50 used in the illustrative process of the invention.

The results of the single stage comparative run and the two stage run of the process of the invention wherein a gasiform efl'luent stream containing carbon monoxide and carbon dioxide was separately withdrawn via line 46 from the first stage reaction zone 30 and a partially unreacted coal-containing liquid efiiuent stream fed via lines 44 and 48 into the second stage reaction zone 50 are set forth in the following Table III:

TAB LE III Single-stage Two stage Weight percent on dry coal system system C1-C hydrocarbons 9. 7 7. 3 O4-400 F. 1iquids 16. 7 17. 8 400 975 F. liquids 33. 5 35. 8 4. 9 5. 2 4. 5 0. 9 8. 2 8. 2 6. 4 14. 6 1. 2 0. 3 19. 2 13. 0. 0. 5 0. 9 1. 0

Total (100 plus H2 consumed) 105 7 104. 6

Oxygen eliminated 22. 4 22. 4 Hydrocarbon liquids:

Weight percent of dry coal 55. 1 58. 8 Barrels/ton of dry coal 3. 45 3. 67 Weight percent distillablo at 975 F"-.. 91. 1 91. 1 Hydrogen consumed:

S.c.f./ton of dry coal 21, 700 17, 500 S.c.t./bbl. liquids produced 6, 280 4, 760

From the above data it will be observed that the amount of water obtained in the comparative single stage process was 19.2 wt. percent based on the weight of the dry coal versus an appreciably lower amount of water obtained in the two stage process of the invention of only 13.0 wt. percent based on the weight of the dry coal and yet the oxygen elimination was 22.4 wt. percent in each case. Moreover, the amount of hydrogen consumed in the comparative single stage process was 21,700 standard cubic feet (s.c.f.) per ton of dry coal (or 10.85 standard cubic feet per pound of dry coal) versus a much lower hydrogen consumption for the two stage process of the invention of only 17,500 standard cubic feet (s.c.f.) per ton of dry coal (or 8.75 standard cubic feet per pound of dry coal). This represents an appreciable reduction in hydrogen consumption, namely, a reduction of about 20%. It will be further noted that the reduction in hydrogen consumption by means of the two stage process of the invention was achieved without sacrifice in the yield of hydrocarbonaccous products. Indeed, the yield of hydrocarbonaceous liquid products was slightly increased by means of the two stage process of the invention (58.8 wt. percent versus 55.1 Wt. percent hydrocarbon liquids on the weight of the dry coal). The increase in liquid product yield is a consequence of the ancillary benefit of staged liquid phase operations upon coal conversion in the ebullated bed system. It is not dependent upon the removal of vapors between the stages.

It will be appreciated that various modifications and changes may be made in the process of the invention in addition to those described above by those skilled in the art without departing from the essence of the invention and that accordingly the invention is to be limited only within the scope of the appended claims.

We claim:

1. A process for reducing the hydrogen consumption in the hydrogenation of a low rank coal having an apparent oxygen content of at least about 15% by weight on the weight of the dry coal which comprises:

(a) drying, grinding and screening said coal to form a coal feed,

(b) slurrying said coal feed with a slurry oil liquid produced in the process,

(0) partially hydrogenating the slurry in a first stage ebullated bed reaction zone with hydrogen in the presence of ebullated hydrogenation catalyst particles,

(d) separately withdrawing a gasiform effluent stream containing carbon monoxide and carbon dioxide and a partially unreacted coal-containing liquid efiluent stream from said first zone,

(e) further hydrogenating said partially unreacted coal-containing liquid efiluent stream in a second stage ebullated bed reaction zone with hydrogen in the presence of ebullated hydrogenation catalyst particles,

(f) separately withdrawing a gasiform efiluent stream and a solids-containing liquid effluent stream from said second zone, and

(g) recovering hydrocarbonaceous products from the gasiform eflluent streams of said first and second zones and from the solids-containing liquid etfiuent stream of said second zone.

2. The process as defined by claim 1 wherein said coal is brown coal.

3. The process as defined by claim 1 wherein the coal feed has a particle size between about 20 and about 200 Tyler mesh.

4. The process as defined by claim 1 wherein the coal to slurry oil weight ratio of the slurry is from about 1:1 to about 1:10.

5. The process as defined by claim 1 wherein the coal feed rate through the first and second stage reaction zones is from about 15 to about pounds per hour per total cubic feet of said two stage reaction zones.

6. The process as defined by claim 1 wherein the hydrogenation catalyst in the first and second stage reaction zones in cobalt, molybdenum, nickel, iron or tin supported on an alumina, magnesia or silica base.

7. The process as defined by claim 1 wherein the hydrogenation catalyst in the first and second stage reaction zones has a particle size between about 6 and about 30 Tyler mesh.

8. The process as defined by claim 1 wherein the first and second stage reaction zones are at a temperature of from about 750 F. to about 950 F. and at a pressure of from about 1000 to about 3000 p.s.i.g.

9. The process as defined by claim 1 wherein the liquid feed rate through each of the first and second stage reaction zones is from about 5 to about gallons per minute per square foot of horizontal cross-section thereof.

10. The process as defined by claim 1 wherein the total hydrogen feed rate through both the first and second stage reaction zones is from about 20 to about 60 standard cubic feet per pound of coal and the separate hydro gen feed rate in each of said two zones is directly proportional to the zone volume thereof.

11. The process as defined by claim 1 wherein the ratio of the volume of the first stage reaction zone to the volume of the second stage reaction zone is from about 1:4 to about 3:1.

9 10 12. The process as defined by claim 11 wherein the 3,183,180 5/1965 Schuman et ,al. 208143 ratio of the volume of the first stage reaction zone to the 3,321,393 5/1967 Schuman et a1 208-10 volume of the second stage reaction zone is about 1:2. 3,519,555 7/1970 Keith et a1. 208-10 References Cited 5 TOBIAS E. LEVOW, Primary Examiner UNITED STATES PATENTS P. F. SHAVER, Assistant Examiner Re. 25 770 4/1965 Johanson 208-10 r U.S. Cl. X.R. 2,860,101 11/1958 Peclpetz 208-10 157 2,987,465 6/1961 Johanson 208-10 

